/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.facebook.presto.sql.planner.iterative.rule;

import com.facebook.presto.Session;
import com.facebook.presto.sql.planner.PlanNodeIdAllocator;
import com.facebook.presto.sql.planner.Symbol;
import com.facebook.presto.sql.planner.SymbolAllocator;
import com.facebook.presto.sql.planner.iterative.Lookup;
import com.facebook.presto.sql.planner.iterative.Pattern;
import com.facebook.presto.sql.planner.iterative.Rule;
import com.facebook.presto.sql.planner.plan.PlanNode;
import com.facebook.presto.sql.planner.plan.WindowNode;
import com.google.common.collect.ImmutableMap;

import java.util.Optional;

import static com.facebook.presto.sql.planner.optimizations.WindowNodeUtil.dependsOn;

public class MergeAdjacentWindows
    implements Rule
{
    private static final Pattern PATTERN = Pattern.node(WindowNode.class);

    @Override
    public Pattern getPattern()
    {
        return PATTERN;
    }

    @Override
    public Optional<PlanNode> apply(PlanNode node, Lookup lookup, PlanNodeIdAllocator idAllocator, SymbolAllocator symbolAllocator, Session session)
    {
        if (!(node instanceof WindowNode)) {
            return Optional.empty();
        }

        WindowNode parent = (WindowNode) node;

        PlanNode source = lookup.resolve(parent.getSource());
        if (!(source instanceof WindowNode)) {
            return Optional.empty();
        }

        WindowNode child = (WindowNode) source;

        if (!child.getSpecification().equals(parent.getSpecification()) || dependsOn(parent, child)) {
            return Optional.empty();
        }

        ImmutableMap.Builder<Symbol, WindowNode.Function> functionsBuilder = ImmutableMap.builder();
        functionsBuilder.putAll(parent.getWindowFunctions());
        functionsBuilder.putAll(child.getWindowFunctions());

        return Optional.of(new WindowNode(
                parent.getId(),
                child.getSource(),
                parent.getSpecification(),
                functionsBuilder.build(),
                parent.getHashSymbol(),
                parent.getPrePartitionedInputs(),
                parent.getPreSortedOrderPrefix()));
    }
}
